Diaphragm spring clutch assemblies generally comprise
a cover assembly which is mounted on the engine flywheel and which comprises a cover housing an axially moveable pressure plate connected in rotation with the cover by means of resilient straps, and a diaphragm spring which provides the load on the pressure plate; PA1 a clutch disc which is splined on the input shaft of the gearbox, and which is clamped between the engine flywheel and the pressure plate; and PA1 a release bearing assembly which acts on the inner periphery of the diaphragm to cause the spring to pivot about its mounting in the cover and thereby release the load on the pressure plate.
The diaphragm spring itself generally comprises an outer peripheral part in the form of a Belleville washer ring which acts on the pressure plate, and an inner skirt which is divided into radial fingers. The spring is mounted for rocking movement between a ring of fulcrums carried by the cover, and the release bearing is adapted to act on the radially innermost ends of these fingers to cause the diaphragm spring to pivot between these fulcrums, thereby releasing the load and disengaging the clutch.
The outer peripheral part of the diaphragm spring usually acts on the pressure plate through an annular fulcrum formed on the pressure plate. In a push type clutch, in which the release bearing pushes the inner ends of the fingers of the diaphragm spring to disengage the clutch, the annular fulcrum on the pressure plate is radially outwards of the ring of fulcrums on the cover. In a pull-type clutch the fulcrums on the cover are radially outwards of the annular fulcrum on the pressure plate.
During the service life of the clutch, as the friction linings of the clutch disc wear, the engaged position of the pressure plate moves progressively closer towards the flywheel. Since the Belleville washer part of the diaphragm spring is always in contact with the annular fulcrum of the pressure plate, the ends of the fingers of the diaphragm spring move progressively, away from the pressure plate in a push-type clutch and towards it in a pull-type clutch. In either case, the load exerted by the diaphragm spring on the pressure plate begins to diminish, and if no action is taken, the clutch will eventually slip, leading to clutch failure.
Adjustment of the clutch to take into account the wear occuring during its service life normally requires that the release bearing should be moved progressively along the input shaft of the gearbox away from the ends of the fingers of the diaphragm spring as the clutch wears. However, this has the effect of increasing the pedal travel and may also increase the pedal effort required during declutching. This requires extra room to be provided in the clutch housing.
Various solutions to this problem have been proposed in order to achieve automatic adjustment of the clutch during its service life, and to provide for constant pedal load. One such arrangement is described in British published patent application GB 2022729A (Borg-Warner). In this proposal, the pressure plate fulcrum surface against which the diaphragm spring bears consists of a separate ring member which is connected to the pressure plate and which is continuously adjustable axially relative to the pressure plate by a series of camming surfaces which move the fulcrum surface outwardly as the clutch friction linings wear. The travel and load characteristics of the diaphragm spring thus remain constant during the service life of the clutch and no adjustment of the release bearing is necessary. However, this arrangement is rather complex in its construction.
In the arrangement described in U.S. Pat. No. 5090536 (Asada) the pressure plate fulcrum again consists of a separate ring member which in this case is screwed into the main body of the pressure plate. Rotation of the ring member in its thread in the pressure plate causes the fulcrum to move away from the friction surface. The ring member is rotated by means of a worm wheel which is operated by a lever and ratchet mechanism responsive to movement of the declutching mechanism. Again, this arrangement is complex both in its construction and operation.
It is an object of the present invention to provide a pull-type clutch assembly which incorporates an automatic wear compensating device.
It is a further object of the invention to provide a pull-type clutch assembly in which the displacement of the diaphragm Spring and its load characteristics remain substantially constant throughout the service life of the clutch.
It is a further object of the invention to provide a pull-type clutch assembly having an automatic wear compensating arrangement which is relatively simple in construction and operation.